1. Technical Field
The present invention relates to a communications network and in particular to a network in which packets are routed on circuits established in a circuit-switched network.
2. Related Art
Conventionally, networks using packet-based protocols such as internet protocol (IP) have functioned on a best-effort basis. As a result, quality of service, as measured by such parameters as packet loss and latency, has varied considerably depending on the loading of network resources such as routers. While such variation is acceptable for some applications, such as Email, it is potentially a barrier to the use of internet protocol for more critical applications such as voice telephony or multimedia conferencing. Accordingly, considerable effort has been addressed to developing guaranteed quality of service mechanisms for internet protocol traffic. One approach is to convert IP traffic for transmission via a circuit-switched network, such as an ATM (asynchronous transfer mode) network and to rely upon the QoS mechanisms inherent in such a network. One example of this approach is the architecture proposed by the ATM Forum and known as MPOA (multi-protocol over ATM). This is described in the specification published by the ATM Forum Technical Committee, “Multi-Protocol Over ATM Version 1.0” AF-MPOA-0087.000, July 1997. This type of approach suffers a number of disadvantages. In particular, it tends to achieve efficient routing only when the end-point of a particular connection lies on the circuit-switched network. Moreover this approach tends to function optimally only within the bounds of single network domain having a common control and management system.